Flow-stimulated K secretion in the distal nephron, including the connecting tubule (CNT) and cortical collecting duct (CCD), is mediated by a Ca2+ and stretch-activated BK channel located in the apical membrane;the BK channel is also critically involved in the renal adaptation to dietary K intake. The density of BK channels in acid-base transporting intercalated cells exceeds that in Na absorbing CNT/principal cells. However, functional measurements suggest that intercalated cells may not have a mechanism to load cells with K to sustain high rates of K secretion into the urinary fluid. The goal of this application is to determine whether BK channels in intercalated and/or principal cells mediate flow-stimulated net K secretion and thereby regulate total body K (and Na) homeostasis. To this end, we propose three Specific Aims (SAs): (1) to confirm, using a selective BK channel blocker, that flow-stimulated net K secretion in microperfused CDs isolated from WT and a mouse strain we will generate with floxed slo1, proposed to be used in SAs 2 and 3, is mediated by the BK channel;(2) to define the role of the 1 subunit of the BK channel in intercalated cells in the in vivo regulation of K secretion in the distal nephron by generating a mouse model with targeted deletion of the 1 subunit of the BK channel solely in intercalated cells within the distal nephron;and (3) to define the role of the 1 subunit of the BK channel in principal cells in the in vivo regulation of K secretion in the distal nephron by generating a mouse model with targeted deletion of the 1 subunit of the BK channel solely in principal cells within the distal nephron. To the extent that the magnitude of distal K secretion determines, in part, Na absorption, and animals with global deletion of BK channel subunits present with alterations in blood pressure, the impact of cell-specific deletion of the BK channel in the distal nephron on Na and K clearances and blood pressure (telemetry) will also be evaluated. The results of proposed studies will define the importance of BK channels in the regulation of renal K (and Na) excretion and maintenance of normal blood pressure, and promises to uncover mechanisms involved in the development and/or maintenance of hypertension and disorders of K excretion. PUBLIC HEALTH RELEVANCE: The proposed studies are designed to determine the physiologic role of BK potassium channels in the distal nephron of the kidney. The studies will define the importance of these channels in the regulation of kidney sodium and potassium excretion and maintenance of normal blood pressure. This work has the potential to uncover mechanisms involved in the development and/or maintenance of hypertension and disorders of potassium excretion.